Application of the aforementioned cobalt cerium compound to various uses that need a cobalt compound having a low resistance is considered. Hereafter, in particular, a case of using in a positive electrode for an alkaline secondary battery will be described.
In recent years, a non-sintered type electrode in which a nickel substrate (nickel foamed substrate) is filled with a paste-like active material is used as a nickel electrode that constitutes a positive electrode of an alkaline secondary battery such as a nickel metal hydride battery, a nickel cadmium battery, or a nickel zinc battery.
Also, with the constitution of a non-sintered type electrode in which a nickel foamed substrate is simply filled with an active material, the electric conductivity decreases in accordance with discharging of the battery, so that a region that does not function effectively as a positive electrode of the battery will be present in not a small amount within the nickel foamed substrate. For this reason, a technique of using cobalt oxyhydroxide which is a cobalt compound having a high electric conductivity is considered.
However, it is now coming to be understood that, when only cobalt oxyhydroxide is used as an electronic conductive additive, there are cases in which an object of improving the electric conductivity is not sufficiently fulfilled.
Specifically, in a case such as when the alkaline secondary battery comes into an over-discharged state to let the positive electrode potential come close to the negative electrode potential or when a state of reverse charging is brought about, the cobalt oxyhydroxide is reduced to decrease the valence number of cobalt and, in accordance therewith, the electric conductivity decreases. Furthermore, when reduced to change into cobalt hydroxide (Co(OH)2), the cobalt oxyhydroxide is dissolved into an electrolyte solution and will no longer function as an electronic conductive additive.
Under such a circumstance, an attempt for restraining the reduction of cobalt oxyhydroxide is also made.
For example, the following Patent Document 1 proposes a construction of adding antimony or the like to an oxidized compound of cobalt.